Polymeric hydrocyanic acids, so-called azulmic acids, and several processes for their preparation have already been described (see Houben-Weyl, Volume 8 (1952), page 261; German Patent Specification No. 662,338 and German Patent Specification No. 949,060). Thus, polymeric hydrocyanic acid is obtained, for example, by heating monomeric hydrocyanic acid to a reaction temperature in a dilute aqueous solution in the presence of a basic catalyst, such as ammonia, sodium cyanate, potassium cyanate or an alkaline earth. After the reaction has started, care is taken that a reaction temperature of, preferably, 120.degree. C. is not exceeded by cooling the mixture (see German Pat. No. 662,338). In a particular variant of this process, further hydrocyanic acid is added to the mixture of solvent, hydrocyanic acid and catalyst in which the reaction has already started (see German Patent 949,060).
These known hydrocyanic acid polymers are brown-black to black pulverulent products which are insoluble in all inert solvents, but which dissolve in 1 N aqueous sodium hydroxide solution, with decomposition, even in the cold. A serious disadvantage of hydrocyanic acid polymers of this type is that when stored, whether under dry conditions or under moist conditions, small amounts of hydrogen cyanide are continuously split off even at room temperature. As the temperature increases, the rate at which hydrogen cyanide is split off also increases. Amounts of hydrocyanic acid which are far above the legally imposed maximum workplace concentration value of hydrocyanic acid of 11 ppm even occur in containers holding azulmic acids no matter how mild the storage conditions. Use in practice of the known hydrocyanic acid polymers thus presents an exceptional danger to the environment and is therefore virtually impossible.
It is also known that hydrocyanic acid polymers can be used as nitrogen fertilizers (see H. Banthien "Synthetische Stickstoffdungemittel" ("Synthetic Nitrogen Fertilizers") in "Handbuch der Pflanzenernahrung und Dungung" ("Handbook of Plant Nutrition and Fertilization") II/2, 1968, Springer-Verlag, Vienna/New York, German Pat. No. 911,018 and Angew. Chem. 72, (1960), pages 379-384). A disadvantage is, however, that hydrocyanic acid is split off from these products, especially under hydrolytic conditions. Their use in practice as fertilizers is therefore scarcely possible.
According to a proposal by Th. Voelker, the brown-black polymeric hydrocyanic acid (azulmic acid) prepared in water has essentially the following formula (see Angew. Chem. 72, (1960), pages 379-384): ##STR1##
A degree of polymerization (HCN) of X=15-24 has been calculated from the oxygen contents of known azulmic acids, so that values of 1 to 4 result for m in formula (I). The maximum molecular weights achieved for the polymers are slightly above 700.